Semiconductor devices for power control are required to have a high source-drain breakdown voltage and a low on-state resistance. For example, a metal oxide semiconductor (MOS) type transistor adopts a trench gate structure to facilitate miniaturization thereof while providing a low on-state resistance. The source-drain breakdown voltage can be increased by using a guard ring structure to terminate an end portion of a transistor structure. However, the miniaturization the structure requires improvements in the structure and the manufacturing method thereof.